The present invention relates to a machine tool monitor (MTM), and more particularly, to an MTM that not only reliably detects tool breaks, but also detects tool wear.
MTMs are shown in U.S. Pat. Nos. 4,636,779, 4,636,780, 4,642,617, and 4,849,741 wherein a tool vibration signal is detected and filtered (averaged) and changes in the mean of the resulting signal are used to detect breakage of the tool. This has been found adequate for reliable detection of the ceramic tool breakage when cutting hard materials, e.g., aircraft engine alloy steel. However, this method is not very reliable when a ceramic cutting tool is lightly cutting such an alloy, or when cutting is performed on ordinary steel alloys with such a tool. In these applications a tool break may produce only a small abrupt shift in the vibration signal that cannot be distinguished from the relatively small abrupt shifts in the mean caused by normal occurrences that do not indicate any tool problems. Further, such MTMs can have difficulty in detecting excessive tool wear, which causes a gradual change in mean vibration signal level similar to the change that can result from normal cutting with increasing depth of cut.
It is therefore an object of the invention to provide apparatus and method for reliably detecting not only tool breaks but also tool wear for various types of cutting tool.